The present invention relates to a method for setting up communications between access points of a switching system.
The invention applies in particular, but not exclusively, to an automatic switch exchange network (PABX) in which access points (lines to terminals or radio bases, links to networks or to leased lines, etc.) are organized into clusters each managed by a cluster control unit (CCU). Each cluster control unit possesses a certain autonomy so as to manage the communications or other provisions of services involving the access points which depend thereon. In particular, the CCU comprises a memory wherein are stored tables containing various data relating to the terminals which are connected to it and making it possible in particular to manage the capabilities available to the terminals.
This hardware architecture gives rise to the software concept of a half-call. The signalling processing relating to the setting up of a communication (or other provision of service) through an access point comprises on the one hand control tasks for monitoring the access point so as to identify events (off-hook, on-hook, dialing, busy, etc.) emanating from an access point and translating them into messages of the switching system and for addressing various commands to the access point (ringing, tones, displays, etc.), and on the other hand call management tasks for processing the requests relating to the access point (as a function in particular of the rights defined in the tables) and for supervising the control tasks for monitoring the access point. The signalling relating to a communication between several access points proceeds through exchanges of messages between the half-calls concerned. Advantageously, the call management tasks use messages according to formats and protocols which are standardized in the switching system, while the access point monitoring tasks deal with the translations required for taking account of the specifics of the various types of terminals or of networks, that can be linked up.
The above architecture is, well suited to the case of fixed terminals connected to the CCU at invariable addresses. The half-call relating to such a terminal can be executed entirely at the level of the CCU to which it is linked (reference CCU). Patent application EP-A-0 790 748 describes a way of adapting it to the case of mobile radio terminals which can enter into communication by means of radio bases connected to visited CCUs distinct from their reference CCUs, the reference CCU of a terminal generally being that where the relevant data relating to this terminal are stored.
The success of networks operating according to the IP protocol (“Internet Protocol”, Request For Comment (RFC) 791 published by the Internet Engineering Task Force (IETF) in September 1981) has led to the, development of real-time protocols (RTP, “Real Time Protocol” and RTCP, “Real Time Control Protocol”, RFC 1889, IETF, January 1996) capable of supporting telephony traffic. Telephony terminals are now available that link up to such networks (“IP terminals”). These IP terminals may in particular take the form of conventional telephones associated with appropriate adapters, of telephone terminals which can be linked directly to the IP network (for example “Webphone”), or microcomputers equipped with telephony software (for example “Netmeeting” marketed by the Microsoft company).
The success of IP networks suggests moreover their use within the domain of switching, and more particularly within the domain of company switching, to connect together various entities of the switching system. The local IP network of a company (Intranet) can thus serve to interconnect distinct automatic switch exchanges. Furthermore, an IP network can advantageously provide a means of connection for IP terminals, so that one can envisage the implementation of voice and data communication systems operating entirely according to the IP protocol. The IP terminals are then managed by call servers connected directly to the IP network. French Patent Application No. 00 08897 describes an example of an architecture of such systems.
The coexistence of the two architectures mentioned above is made indispensable by the need to take account of the current infrastructures in the process of migration toward networks operating entirely according to the IP protocol.
In an architecture combining PABX networks of the type indicated above and packet switching networks, certain of the CCUs (“Gateway CCUs”) are then equipped with gateway interfaces with a packet switching network such as an IP network. These gateway interfaces perform the conversion of the streams exchanged between the two types of network, in such a way as to comply with the manner of operation of a media gateway (or MGW) and of its controller (“Media Gateway Controller” or MGC) as described in the TIPHON (“Telecommunications and Internet Protocol Harmonisation Over Networks) project of the ETSI (“European Telecommunication Standard Institute”). Such a gateway interface provides an access point connected to the IP network, and makes it possible moreover to implement communications over the IP network involving analog or digital “conventional” terminals that are not directly linked to the IP network, without however necessarily comprising an access point for these “conventional” terminals. Conversely, an MGW typically provides an access point for various types of “conventional” terminals, and comprises an access point connected to the IP network.
It is thus possible to envisage the setting up of communication paths between all types of terminals carried or otherwise by the IP network. Patent application PCT/FR00/02740 describes a way of optimizing the setup of the communication path when a gateway interface with an IP network is involved.
The choice of the communication path can be made on request by a topology server, as a function of criteria specific to the system, and information regarding the location of the terminals involved in the communication.
This process, when it leads to the setting up of a communication path between the PABX network and the packet switching network, uses resources of the gateway CCU while communicating.
However, such flexibility gives rise to cost constraints, in particular with the prospect of a rapid increase in the traffic over packet switching networks. Specifically, the large number of conventional terminals installed on existing traditional networks benefiting from updating with interfaces to packet transmission networks makes it possible to forecast massive use of gateway interfaces, so that it is desirable to optimize the switching systems with a view to optimal use of these gateways, the unit cost of which is relatively high.
For example, the possibility of making simultaneous multiple calls from one and the same terminal, conventional or IP, may lead to the reserving of several gateways, each for a simple call, while the user will use just one of them at a given instant. This example is in particular that of operator stations in a communication system.
An object of the present invention is to optimize the use of the resources mobilized by communications in networks using gateways of the kind indicated above.